Tracking and registration of an eye position is known to be used for several applications in ophthalmic surgery and diagnostics. However, the majority of solutions offer only partial results, in the sense that they are only applicable within the same device or within a particular combination of devices. The current ophthalmic care procedures are complex processes that involve a plurality of tools in varying contexts that create significant impact on the eye appearance. Some of these impacts even prohibit the application of current registration techniques. Being able to relate the various measurements in a unified way presents a significant challenge.
Currently, there are multiple new surgery techniques that imply a fully fixated eye relative to the treatment device, e.g. femtosecond laser for corneal procedures, microwave deforming devices for corneal treatments, or femtosecond laser for cataract surgery. All these surgery techniques have in common the fact that the treatment zone is placed relative to a suction ring on the eye. In the coordinate system of the suction ring, the eye can be treated with automatic means that achieve treatment positioning precision that is far better than any manual one.
This means that using a suction ring coordinate system the eye can be treated with a spatial precision that is far better than the mechanical precision of a surgeon. But: In the overall diagnostic-treatment process, the placement of the suction ring on the eye may induce significantly higher errors than the reduction of the error which automated treatment may achieve, because:                a) The Placement of the ring is not accurately controllable:                    The procedure is done manually by the surgeon, thus being limited by general human mechanical abilities. During the suction process, the suction ring slides slightly on the cornea until it is fixed relative to the eye, thus always introducing errors with respect to the desired position.                        b) Actual placement of the ring is difficult to measure:                    The eye is deformed by the unnatural pressure, which impacts the capabilities of measuring the eye biometry (e.g. corneal shape) after the suction ring is placed. Natural landmarks on the eye (e.g. sclera features, limbal border) are covered by the tool mechanics (e.g. suction ring). Therefore a manual visual alignment of the ring by the doctor is hard to achieve.                        c) Manual measurement and adjustment of treatment zone takes time:                    The suction ring placement time and the time for manual adjustment of the treatment zone can be longer than the treatment time itself. Stress and dehydration of the patient's eye may interfere with the physical and mechanical assumptions for the (laser) treatment.                        
Consequently, the high precision of the new generation treatment devices is an instable promise, due to the errors and uncertainties induced as mentioned before in connection with the placement of the suction ring.
The proof of clinical outcome improvement with these new generation devices depends on a reliable basis for documenting and analyzing surgery with post-surgery results. It is therefore an object of the invention to provide a method and an apparatus, which can reduce these negative effects of the errors induced by the suction ring.